Selecting the Right Electric Tugger for Your Application

By: Ray Erbe, Contributor

Today, companies are struggling to increase productivity, while dealing with a shrinking and older labor force. In the world of material handling, these factors are driving material transport solutions that increase efficiency and improve the ergonomics of the workplace. Twenty years ago, the go-to solutions available for moving materials were forklifts and pallet jacks, while scissor lifts provided a solution for lifting materials in a work cell. These solutions are still available today, however the number of other motorized solutions for moving materials has exploded. In this article we’ll explore one of these solutions, electric tugger machines.

Why Choose an Electric Tugger Solution?

One of the key advantages of electric tuggers is their diverse, broad range of uses. These machines can be customized to meet the specific needs of your business, with a variety of attachments and accessories available. For example, you can choose from a range of towing hitches and couplers to accommodate different types of loads. With some models, the tugger can even hitch to a cart without having to attach a hitch to the cart itself. This flexibility means that electric tuggers can be used in a wide range of settings, from warehouses and distribution centers to airports and hospitals.

Selecting the Right Electric Tugger

The most significant question that needs to be answered is: which tugger will I need to move my loads?

Let’s assume that the weight of the load you are trying to move, the weight of the cart, plus the weight of the material being moved is 5,000 pounds. Your first thought might be, “This is simple, just pick a tugger that has a 5,000-pound rating and be done.” This solution may or may not work for your application. Why is that?

Drawbar Force

The Pony Express AC Tugger has a towing capacity of 100K lbs. Image courtesy of Electro Kinetic Technologies.

To explain drawbar force and its relevance to moving a payload, let’s picture diagram of a horse pulling a cart. When the cart is not moving, the horse needs to apply a force in a forward direction to get the cart moving. Once the cart is moving and the speed is constant, the drawbar force drops significantly by a factor of two or more, depending on the surface material.

For the horse to be able to generate enough force to move the cart, it needs enough weight on its hooves for traction to prevent them from slipping on the surface. If it does slip, the horse will not be able to move the cart.

In material handling applications, the horse is replaced by an electric tugger and the wooden cart will likely be made of steel with two fixed and two swivel casters. The surface is no longer dirt, but most likely concrete. Very much like the horse, the electric tugger can only generate a certain level of drawbar force. We can further define two levels of drawbar force: one instantaneous duration (1 to 3 seconds) to get the cart moving, or a continuous duration (60 minutes) drawbar force to keep the cart moving. The most significant one of these in defining whether a tugger will move your load is instantaneous drawbar force.

Now that you have this information you can answer the question, “Will the tugger move my load?” All you need to know is how much drawbar force is required to get your payload moving. Keep in mind that if you have a fleet of carts with various sizes and materials of casters, the amount of drawbar force will vary between carts. The reason for this variance is the physics of the wheels on the casters and the coefficient of friction of the wheel material.

As you can see from the chart pictured, the variability of the towing capacity of a particular tugger with a defined maximum drawbar force is a function of the caster wheel diameter and material. As an example, if you selected a tugger with this performance curve, its towing capacity would be less than 2,000 lbs. with a cart having 8” diameter molded rubber casters. The capacity would be 8,000 lbs., however, with the same diameter of phenolic casters.

In generating this curve, the tugger manufacturer should have also taken into consideration whether the tugger had enough ballast weight on its own or through load transfer to obtain the defined drawbar force on the surface specified; in this case flat, dry, concrete. If this is not taken into consideration, then the tugger machine’s wheels will spin with a resultant reduction in available drawbar force.

Diagram 1: Tugger Towing Capacity vs. Caster/Wheel Diameter, shown on various surfaces. Graph courtesy of Electro Kinetic Technologies.

Drawbar force is an important factor when selecting a tugger for your application, however consideration should be given to some other factors that are important as well to the performance of the machine in your specific application.

• How does the tugger connect to my cart? Can this connection be customized for my application?
• Can the tugger operate on my floor surface?
• I have inclines to navigate. How will this impact my tugger selection?
• How easy is it to maneuver the tugger in tight spaces?
• Does temperature and ingress rating (IP) of the tugger match my environment requirements?
• How long will the batteries last? Keep in mind this will vary depending on battery technology, and actual usage of the tugger machine.
• What is the recharge time of the batteries?
• What battery technologies are offered?
• What training is needed for my operators?

Electric tuggers are a versatile and efficient solution for material handling tasks in a wide range of industries. With their ability to be customized and configured to meet the specific needs of your business, they can help you improve productivity, reduce labor costs and increase safety. Whether you’re looking to move heavy machinery, pallets, carts and so much more, electric tuggers are often a perfect choice for your operation.  WMHS

Ray Erbe has worked in industrial automation product development since 1978 and has served as President & Chief Technology Officer of Electro Kinetic Technologies since 2009. Electro Kinetic Technologies (www.ek-tech.com) is a U.S.-based company that designs and manufactures motorized ergonomic solutions to move and lift materials up to 100,000 lbs.